1. Field of the Invention
The present invention relates to an electronic camera.
2. Description of the Related Art
A first prior art concerning an electronic camera is a technique which relates to a timing generator.
A circuit called a timing generator is used in an electronic camera. The timing generator generates a timing signal required for a CCD, an imaging circuit and others to operate.
This timing generator is conventionally produced based on a dedicated hardware logic according to a specification of an imaging element used in the electronic camera (Japanese patent application laid-open No. 2000-165758).
Under the circumstance in recent years that the imaging element is graded up in a short period, however, designing and manufacturing a new timing generator every time the imaging element is updated require a large amount of cost.
Thus, there is provided a general-purpose timing generator which incorporates a memory, and which can program values such as the timing-pulse cycle of timing signals and can generate timing signals that meet the specification of an imaging element.
However, in order to actually drive the imaging element, various timing pulses are required. Therefore, when supplying a timing pulse of the imaging element by using a general purpose type timing generator including an internal register capable of setting a program, cycles, levels, duties and the like of all the timing pulses must be set from the outside.
In a conventional dedicated timing generator in which a logic is constituted by using hardware, the number of internal registers which must be set from the outside is very small. Therefore, a time required for setting of the internal registers is ignorable, and a setting time is not a problem.
However, using the general purpose type timing generator including the internal registers capable of setting a program requires a very large amount of time which is several-tenfold of a setting time needed in the prior art. Therefore, if a setting operation of the internal registers is performed after each circuit such as a timing generator or an imaging element in an electronic camera is started like the prior art, a delay is produced in starting of the entire electronic camera, thereby causing a reduction in the operability.
A second prior art concerning an electronic camera is a technique which relates to switching of a substrate voltage.
In a conventional camera, there is used a technique which changes a handling electric charge quantity by switching a substrate voltage Vsub of an imaging element in accordance with an imaging condition of the electronic camera in order to obtain an imaging signal with a required resolution (Japanese patent application laid-open No. 5-211320).
The imaging element is configured in such a manner that electric charges are absorbed from a photosensitive element to a substrate side by, e.g., an overflow when electric charges which are more than a fixed quantity are generated in the photosensitive element, thereby preventing a reduction in blooming, smear or the like. Such a stored electric charge quantity in the photosensitive element as that the overflow is thereby started is called a handling electric charge quantity.
However, there is a problem that an image signal level fluctuates when the substrate voltage Vsub is switched, a signal processing circuit on a rear stage, especially a clamp processing circuit thereby erroneously operates, a noise is temporarily generated and signal shading is generated in an image.
Therefore, in order to avoid the signal shading in an image due to a clamp miss, preventing switching of the substrate voltage Vsub can be considered. However, increasing the handling electric charges by switching the substrate voltage Vsub as described above is required in order to obtain an image with less noises, and a possibility that an image quality is lowered due to blooming or the like is high when the substrate voltage Vsub is not switched.
A third prior art concerning an electronic camera is a technique which relates to an n:1 (n is a natural number not less than 3) interlace read type imaging element.
In a conventional electronic camera using a 2:1 interlace read type imaging element, unnecessary electric charges in a transfer path of the imaging element are flushed at a high speed, and the electric charges of each pixel are then read into the transfer path and transferred through the transfer path at a regular speed, thereby taking out signal electric charges (Japanese patent application laid-open No. 2000-165758).
Further, the conventional electronic camera adopts a technique by which the handling electric charges are controlled by switching the substrate voltage Vsub based on a monitor mode which is a mode for displaying a moving picture and a still mode which is a mode for taking a still picture in accordance with each shooting mode of the electronic camera in order to obtain an imaging signal with a required resolution.
Furthermore, these techniques can be likewise applied in an electronic camera using the n:1 (n is a natural number not less than 3) interlace read type imaging element.
In the n:1 (n is a natural number not less than 3) interlace read type imaging element, however, there is a problem that unnecessary electric charges remain when flushing is carried out at a high speed.
Moreover, in the n:1 (n is a natural number not less than 3) interlace read type imaging element, there is a problem that a clamp miss of a black level is generated due to switching of the substrate voltage Vsub and the signal shading is produced in an image.